Understanding Memtest86 Results

For the last month or so, I've been plagued by blue screens whenever a significant amount of data is transferred through USB. This can be especially frustrating, given my wireless adapter is USB and is triggering a BSOD whenever I try to do some heavy browsing. I've planned to do a fresh install before resorting to more costly options, but before that I decided to try out memtest86 to see if I could narrow down the cause.

I'm getting some mixed results however, and I'm not quite sure what to think of it. My motherboard has two slots for RAM and I have two 4GB sticks to fill them. I've done a pass with each configuration and the results are as follows. For reference, A and B will refer to the RAM slots, and 1 and 2 will refer to the sticks.

1 in A, 2 in B - 98 Errors (initial setup)
2 in A, 1 in B - Crapton of Errors*
1 in B - 0 Errors (ran twice)
2 in B - Crapton of Errors*
1 in A - 0 Errors
2 in A - 0 Errors
1 in A, 2 in B - Crapton of Errors*

*Didn't let these configurations complete a pass as the errors were piling well pass 15000+.

Given the results and my limited experience, I see three possible causes. At first I was thinking that it was a bad stick, since 1 ran with no errors in both slots, but then so did 2 in slot A. The second option is a bad slot, but then how did stick 1 run okay in both? If neither of these are the issue, then I can only assume that there is a bigger underlying problem related to the motherboard.

I'm also worried that I might have damaged something during the testing, as I'm getting a lot more errors (read crapton) despite having the same configuration I started with.

I'd really like to think it isn't the motherboard, but given the BSOD and now the memtest results it is starting to look that way. However, I'm no expert and this is my first build, so I would appreciate any input on the matter. The computer was built about 9 months ago and hasn't had any issues until now. I can provide more specifics on the build if necessary.